Field of the Invention
The present invention relates to a method for detecting impermissible operating states in a hot-air clothes dryer, and to a dryer in which such a method is implemented.
In conventional clothes dryers, clothes in a drum that as a rule rotates are dried by passing a flow of heated air through the drum and thus through the clothes, the flow being capable of drawing moisture from the damp clothes, thereby gradually drying the clothes.
The air flow supplied is heated in a supply line upstream of the drum by means of a suitable heating device. After passing through the clothes in the drum, the air is either discharged to the outside (air-exhaust clothes dryer) or delivered to a heat exchanger, in which the air is cooled down and the moisture precipitates out as condensate.
In both types of clothes drying, similar problems arise in terms of safe, reliable dryer operation.
The clothes drying process is such that the incoming air is heated and flows through the clothes, and depending on the degree of moisture of the clothes and on the temperature of the air itself, the air draws a corresponding quantity of moisture from the clothes. It is a requirement that after the clothes attain a certain degree of dryness, excessive heating of the incoming air stream and thus both overheating of the clothes on the one hand and overheating of the dryer itself on the other are avoided.
In the prior art, many solutions to this problem have been offered but in the final analysis have proved unsatisfactory.
There has become known from German published non-prosecuted patent application DE 16 10 314 a method for automatically controlling the drying process until a desired degree of dryness is attained. This is effected as a function of gradients in the rising temperature in a clothes drying system, in which during or at the end of the drying process the difference between the temperature of the incoming air and the outgoing air is ascertained, and the change over time in this difference is utilized as a criterion for turning off the heating device. This method requires at least two temperature sensors with corresponding control, and the controller does not turn off the heating process until permissible maximum temperature values are exceeded.
U.S. Pat. No. 4,412,389 (German patent DE 30 30 864 C2) discloses a method for automatically controlling the drying process in a clothes drying system and a device for performing the method. There, a suitable length of operation is calculated in comparison with an imagined period of operation of the drying process, and the drying process is controlled accordingly.
However, that prior art process is disadvantageous in that the drying process is not turned off until permissible operating states are attained, and hence it is not reliably possible to preclude possible damage to both the clothes and the dryer appliance.